The invention relates to a method for fabricating integrated sensors.
Micromechanical sensors based on CMOS-compatible fabrication techniques often require, due to physical limitations and measurement technique limitations, large vertical-lateral aspect ratios in combination with large areas of the sensor elements. In order to produce these aspect ratios, large layer thicknesses typically of more than 1 xcexcm are used, which are not fabricated in the course of a customary fabrication process for CMOS circuits. Therefore, if a micromechanical sensor is intended to be integrated with electronic components of a drive circuit, the problem arises of how to deal with the thick sensor layers within the CMOS process. After the patterning of such layers, considerable problems occur during subsequent phototechnology steps with regard to whole-area and uniform photoresist coating. The photoresist is applied using a so-called spin coating method, during which high steps on the processed surface prevent the photoresist from spreading uniformly when the photoresist, which is initially applied only in the center, is spun. As a result, it becomes necessary to use very large quantities of photoresist or to dispense with high steps in the surface topology.
An overview of the field of micromechanical sensors in the last 35 years is provided by S. Middelhoek et al. in xe2x80x9cReview Article Silicon Sensorsxe2x80x9d, Meas. Sci. Technol. 6 (1995), 1641-1658. By way of example, the fabrication of a micromechanical sensor on a substrate is described in which use is made of sacrificial layers that are deposited on the substrate and are removed again after that part of the micromechanical sensor which protrudes from the substrate has been produced. E. Yoon et al. describe in the article xe2x80x9cAn Integrated Mass Flow Sensor with On-Chip CMOS Interface Circuitryxe2x80x9d, IEEE, Transactions on Electron Devices, Vol. 39, No. 6, June 1992, 1376-1385, various types of micromechanical sensors and methods for fabricating them, including a pressure sensor. The substrate used in this case is processed on both sides.
German Patent Document DE 43 32 057 describes a method for fabricating a micromechanical sensor in which a body is formed with an insulating layer provided on a substrate and a monocrystalline silicon layer provided over the insulating layer, the silicon layer including a given doping. Trenches are etched in the silicon layer down to the surface of the insulating layer. The trench walls are doped. A transistor configuration is produced in a first region of the silicon layer. The insulating layer under a second region of the silicon layer is removed.
German Patent Document DE 44 14 968 describes a micromechanical component and a method for fabricating the component. An integrated circuit is produced in the substrate on which the component is produced. The metallization layer of the integrated circuit is simultaneously used as a part of the micromechanical component.
It is accordingly an object of the invention to provide a method for producing an integrated sensor which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which is suitable and practicable for integrating micromechanical sensors having a high aspect ratio with electronic components. In particular, it is an object to provide a method which is suitable for an implementation within a CMOS process.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating an integrated sensor, which includes the steps of:
fabricating, in a first step, on a top side of a semiconductor body, a structure of at least one electronic component and fabricating, in the semiconductor body, a recess, a depression or a region with a top region being lowered relative to an adjoining region by removing material of the semiconductor body;
depositing, in a second step, a layer in the recess, the depression, or the region with the top region lowered relative to the adjoining region, such that the layer projects above the top side of the semiconductor body in a vertical direction;
structuring, in a third step, the layer for fabricating a micromechanical component; and
completing, in a fourth step, the at least one electronic component and the micromechanical component including electrical contacts and interconnects.
In accordance with another mode of the invention, in the first step, firstly the structure of the at least one electronic component is fabricated and the structure of the at least one electronic component is covered with a protective layer, and subsequently the recess, the depression or the region with the top region lowered relative to the adjoining region is fabricated by removing the material of the semiconductor body.
In accordance with yet another mode of the invention, in the first step, firstly, the recess, the depression or the region with the top region lowered relative to the adjoining region is fabricated by removing the material of the semiconductor body, and subsequently the structure of the at least one electronic component is fabricated.
In the method according to the invention, recesses or depressions are created in the substrate formed by a semiconductor body, with the result that sensor components which are fabricated therein are partially sunk or lowered. The recesses or depressions or regions in which the top side of the semiconductor body is lowered relative to an adjoining region are fabricated by removing semiconductor material from the semiconductor body, preferably by etching, before or after electronic components are fabricated in the remaining region of the top side of the semiconductor body. If the semiconductor material is not removed until after the electronic components have been fabricated, the latter are covered with a protective layer. A layer is deposited in the region of the recess or depression, the layer being provided for the patterning of the essential component parts of the sensor element and preferably being polysilicon. This layer projects above the top side of the component by between 20% and 80% of the layer thickness, preferably between 40% and 60% of the layer thickness, since, to enable simple fabrication, it is advantageous if the layer projects above the top side approximately by half.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for fabricating integrated sensors, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.